At present, in the latest technical specification TS33.328 v1.1.0 about the media security of an IP multimedia subsystem (IMS) in 3GPP, it is proposed to use a solution based on a key management server to protect the end-to-end security of IMS media stream.
The solution in TS33.328 v1.1.0 is based on concepts of the key management server (KMS) and “ticket”. The existing solution can be simply described as follows:
a calling party of a session requests a relevant key and a ticket from a KMS at first, and in this ticket, the relevant key obtained by requesting from the KMS by the calling party is contained in the ticket after being encrypted;
the calling party, after obtaining the relevant key and ticket, sends the ticket to a called party;
since the called party cannot decrypt the ticket to obtain the information contained therein, the called party continues to send the ticket to the KMS, and the KMS decrypts the ticket and returns the relevant key in the ticket to the called party;
the calling party and the called party can communicate by using the media stream encrypted by adopting the common relevant key.
However, there may be not only one KMS in a network, and when there are a plurality of KMSs, which one of the KMSs will be used by the user relates to an allocation mode of the KMSs.
The allocation mode of the KMSs has no more than two modes: one is that a user itself pre-configures one KMS but an IMS core network network element does not participate in; the other is that the IMS core network network element participates in and allocates to a user a KMS used by the user.
In the related art, an identification of the KMS is transmitted in a signaling by a plaintext, i.e., the used KMS ID by the plaintext is added into an INVITE request of initiating the session by the calling party; and after intercepting the signaling, a lawful intercepting device obtains the required key material and knows the KMS used by the user by the plaintext, and then asks the relevant key material from the corresponding KMS. It can be seen from that the solution in the related art depends on the security of a signaling plane, so the safety factor is lower.